No. At the start of your monthly bundle, we convert unused calling minutes into extra data: 5 megabytes per unused minute. You don't have to pay anything for this. You'll only pay when your data bundles are completely exhausted. The rate will then be € 0.10 per MB. Are you abroad? Then the roaming rates will apply.
Watch out: this advantage only applies to subscriptions that were contracted before 10/7/2017.